Hi
Fade through white works and exports here...:blink:

"........I'm using the same version, it's 10.24. No transition is overlapping from my knowledge......"
If you are adding a transition between two different video clips you should normally see a window that asks if you want to overlap the clips or use a still image from each clip as the transition image that fades in or out. The overlapping option shortens the timeline slightly but is smoother. You may the feature inactive in your Option/Editing Try setting it to "Ask Me" so you get the choice.
It's odd that fade out -fade in over a white blank clip doesn't work. That's pretty standard fare. The fade out is for the first clip and is selected using the FX box and choosing that effect. The fade in for the next clip is the same. If you look down the effects list after you have clicked the FX box for the clip you will see the different fade options...

Give it a try with the two clips on track 2 and the white blank on Track 1 The white blank is pulled out to be the same duration as the two fades. as shown in my first post.
Nat